For the purpose of this application, it is noted that the term "heavy-duty industrial scale" is intended to refer to the numerous types of scales that are commonly used for weighing of large objects and heavy loads. Among these types of scales are warehouse scales, truck scales, railroad scales, grain dump scales, etc. Typically, such scales utilize a massive weighing platform which is coupled via a load transmission system to a weight indicator.
Generally, there are two types of load-transmitting systems that are utilized in heavy-duty scales. One system employs a transducer on a loaded beam and strain guages to convert elastic strain of the beam into electrical signals which are proportional to the load on the transducer. Other types of scales utilize a purely mechanical system for transmitting the load on the weighing platform to a weight indicator through mechanical movements that are a function of the load on the platform.
In mechanical systems, to avoid problems of side loading of the weighing platform, as might occur from a vehicle passing onto and off of the platform, link suspension assemblies have been utilized to interconnect the weighing platform load-transmitting beam to a lever of a lever assembly. In the weighing scale of U.S. Pat. No. 1,167,311, a single-link suspension system is utilized wherein the load from a platform girder is transmitted, by way of a platform supporting member, to a single link suspension member via a universal coupling at a bottom of the link; the top end of the link hanging on a saddle block that forms part of a knife-edge type pivot along with a knife-edge part carried by the main lever. However, despite the presence of a universal connection, this type of suspension, effectively, can only provide two degrees of freedom in the horizontal plane.
A second type of link suspension system commonly used in heavy-duty mechanical scales is a parallel link suspension system. The parallel link suspension system is well known and is found, commercially, in Fairbanks Morse "Type-S" scales produced by the Fairbanks Weighing Systems Division, of Colt Industries, St. Johnsbury, Vt. These scales encompass numerous types of heavy-duty industrial scales, including all of the types noted above. In the parallel link suspension system, a mount is connected to a platform load-transmitting beam and a pair of parallelly disposed spaced links interconnect the mount with a saddle block carrying one part of a knife-edge type pivot, the other part of which is carried by a main lever. In such a system, two pivots are created, a fulcrum pivot and a load pivot. The fulcrum pivot is defined by a knife-edge and bearing block and serves to transmit the load on the mount to ground as well as allowing an arm of the mount to rotate under a load applied to it. The load pivot transfers the applied load to the fulcrum through the parallel links which form a motion-isolating linkage. Some rotation is possible between the links at their upper and lower connecting points, but such will allow only two degrees of horizontal freedom without affecting the accuracy of the scale or the life of the pivot. Pivot life can be adversely affected by rocking or horizontal movement of the bearing block on the knife edge.
Additionally, since the multiple of the main lever is a function of the fulcrum distance (a shorter fulcrum distance producing a higher multiple) and since the fulcrum distance is a function of the width of the suspension system formed by the mount and links (a shorter width enabling a shorter fulcrum distance), link suspension systems inherently impose limits on the attainable fulcrum distance and lever multiple. Similarly, since link suspensions extend a significant distance below the associated main lever, they increase the overall height of the scale and, accordingly, the amount of space required for installation.
In contrast to the noted suspension systems used in purely mechanical scales, many electronic scales have utilized a suspension arrangement in the form of a single pin that is arranged to bear on the end of a load cell and extends vertically to contact an opposing flat surface. Shallow, spherical-shaped ends are provided on the rocker pins to provide a free-floating motion to the scale platform (that is limited by bumper checks) in order to minimize side loading of the load cell. An example of such an arrangement can be seen in German Auslegeschrift No. 1 806 668.
A rocker pin suspension is simpler and more compact that a link suspension; however, up until now, no workable arrangement has existed for adapting the rocker pin suspension concept utilized in electronic scales to purely mechanical lever scales of the type using link suspension systems. For example, if a single rocker pin, as used in the noted prior art electronic scales, were used at the load pivot of each main lever, such an arrangement would be unstable.
From the foregoing, it is apparent that a need has existed for a way in which heavy-duty industrial scales of the mechanical lever type can be provided with a simpler and more compact suspension than the existing link suspension systems and that affords more than two degrees of freedom of movement in a horizontal plane, while being adaptable to the requirements for a wide range of different sizes and types of scales.